a) Field of the Invention
The invention is directed to a video projection system with at least one light source which can be controlled in intensity and which generates at least one light bundle and with a deflecting device which deflects the light bundle sequentially to produce picture points of a video picture on a screen by picture and line scanning.
b) Background Art
A video projection system of the above type is known from "Funkschau" 1970, issue 4, page 286. This is a video projection system for color pictures whose different color signals are produced by lasers and in which the light bundles emitted by the lasers are changed in intensity corresponding to the color value of each picture point of the video picture by means of light modulators. The light bundles emitted by the light modulators are combined by means of dichroic mirrors to form a common bundle of rays which is deflected via a mechanical-optical deflection system for scanning of picture and lines and is projected on a screen. With very large screen sizes, the lasers must be designed for correspondingly high outputs, which leads to a considerable space requirement for the lasers which can be employed. In addition to the size of the lasers, the cooling required by these lasers presents another problem standing in the way of a compact construction. Therefore, video systems of this type are costly and require a large amount of space so that they cannot be used in the home, for example.
The above-mentioned article from "Funkschau" also describes another video projection system which requires even more space, since the different colors must be filtered out along a prismatic path. Moreover, the vertical deflection in this system works with a vibrating mirror. This video projection system thus requires additional beam splitters and additional mirrors in the deflecting device which increases the space requirement as well as construction costs.
A suggestion for realizing a compact construction in a video system is found in DE 34 04 412 A1 which describes a digital, flat large color television screen. In this video system, the picture points of a video picture are projected onto a screen by means of light-guiding or optical fibers which spread out in the direction of the screen. Spreading the optical fibers can produce on the screen a picture which is larger than the primary image. Further, the use of optical fibers makes it possible to choose the location for the light generation independently of the position of the screen so that the space requirement can be minimized.
However, a disadvantage in this technique consists in that an optical fiber is required for each picture point. Thus, in this example, 519,792 optical fibers are required for transmitting the picture. Moreover, these fibers must be bonded together in an ordered manner. The cost of producing such a system is therefore extremely high and the work-load per optical fiber is low. There is also a high rejection rate involved in production due to the required exact adjustment of the optical fibers relative to one another.